The present invention relates to a heat sink for cooling a heating element, e.g. a semiconductor such as an IC, a CPU, or an MPU, or an electronic component having the heating element. The invention also relates to a method of manufacturing the heat sink and to a cooling apparatus including the heat sink and a cooling device like a fan for cooling the heating element.
Electronic apparatus have recently generated larger amounts of heat due to having electronic components such as semiconductors integrated at high density and employing operation clocks of high frequency. There has accordingly been concern as to how to maintain an electronic component within an operation temperature range in order to operate normally. The integration of an MPU is drastically enhanced, and a frequency of the MPU is increased. Heat radiation is thus important for stabilizing operation and ensuring an operation life.
A cooling apparatus including a heat sink and a fan having a motor combined generally radiates heat from the electronic apparatus. The heat sink has a larger heat radiation area and efficiently conducts heat to a coolant such as air. The fan forcibly supplies the coolant to the heat sink.
A conventional cooling device will be described hereinafter with reference to FIG. 13A through FIG. 16B.
FIG. 13A and FIG. 13B are perspective views of conventional heat sinks. FIG. 14A and FIG. 14B are a top view and a front view of a conventional cooling apparatus, respectively. FIG. 15A is a perspective view of another conventional heat sink, and FIGS. 15B and 15C are a front view and a side view of another conventional cooling apparatus, respectively. FIG. 16A and FIG. 16B are a front view of the conventional cooling apparatus and a graph showing a heat-radiation performance. Thus, the heat sinks are of various types, including: a plate type heat sink shown in FIG. 13A that includes many plate-like fins 1a, i.e., thin plates, disposed on a base plate 2a constituting a heat conducting unit; a column type heat sink shown in FIG. 13B that includes many columnar fins 1 disposed on a base plate 2a; and a tower type heat sink shown in FIG. 15A that includes many plate-like fins 1a, i.e., thin plates disposed perpendicular to a heat conducting plate 2. These types of heat sinks are mainly made of material such as aluminum or copper having high thermal conductivity, and are manufactured by extrusion molding also called drawing molding), cold forging, die casting, or thin plate laminating. For being mounted to a heating element, the heat sink may be disposed directly on a heating element 3 as shown in FIG. 14C, and a thermal diffusion plate 2c may be disposed between the heating element 3 and the heat sink as shown in FIG. 14B. The thermal diffusion plate 2c conducts heat from the heating element 3 to the heat sink, diffuses the heat, and protects the heating element. In a cooling principle of the cooling apparatus, as shown in FIG. 14B, the heat generated from the heating element is conducted to the columnar fins 1 through the heat conductive base plate 2b made of e.g. aluminum having high thermal conductivity. Then, the heat is further conducted, at the surface of columnar fins 1, to air supplied from the cooling fan 4, diffused into the air.
For an improved performance of the cooling apparatus, the heat is favorably diffused uniformly to an entire heat-conducting unit and radiated from the radiating fins. Regarding the conventional plate-type or column-type heat sink shown in FIG. 13A or FIG. 13B, if the heating element is much smaller than the heat-conducting unit and contacts the heat-conducting unit over a small contacting area, the heat from the heating element is intensively conducted to the radiating fins in the region directly above the heating element, but is relatively hardly conducted to the radiating fins away from such region. Therefore, the radiating fins may not totally function.
When airflow is constant around the radiating fins, radiating capacity increases with an increase of the number of fins and surface area. However, as a total cross-sectional area of the radiating fins in a unit area increases, a part in which air can flow, for example, an air inlet area 18 denoted by oblique lines in FIG. 14A decreases. Total incoming airflow can therefore decrease to degrade radiation performance. In other words, simply increasing number of radiating fins may not improve a cooling effect.
It is most important for the cooling that the heat from the heating element is efficiently conducted to the largest possible range of radiating fins, as discussed above. An improvement in the radiation performance is desired. A tower-type heat sink shown in FIG. 15A, for example, conducts the heat generated from the heating element directly to the upper part of the heat sink through a heat-conducting plate at the center. The heat is diffused in planate by plate fins formed vertically (i.e. perpendicularly to the axis of the heat-conducting plate). The heat diffused in planate from both sides of the thin plate is generally radiated into the air naturally by air cooling.
The conventional cooling apparatus, however, hardly cool an electronic component such as a semiconductor processing at a high speed which generates more heat. A high heating electronic component like an MPU especially cannot perform sufficiently or causes thermal runaway, thereby causing abnormality in the electronic apparatus. The cooling apparatus itself may be relatively enlarged to improve its cooling ability for the increasing heat. However, the size of the electronic apparatus inevitably restricts the size and weight of the cooling apparatus. The tower-type heat sink shown in FIGS. 15A-15C generally includes the heat conducting plate 2 conducting heat from the heating element to each fin more efficiently than the plate-type or column-type heat sink shown in FIGS. 13A and 13B. The tower-type heat sink has a high heat conduction efficiency because of the structure of the heat sink, but tends to stagnate air due to the piled plate fins 1a. A cooling fan is disposed on a side of the tower-type heat sink in consideration of air flow, because simply disposing the cooling fan in the upper part is hardly effective. Even in such a case, the cooling fan is attached to a side of the heat conducting plate in an upright posture in the width direction of the heat conducting plate 2. A section of the heat conducting plate 2 therefore disturbs the air flow from the fan and restricts incoming air flow. Since shaped like plates, the fins hardly provide a sufficient surface area. As a result, even the tower-type heat sink hardly improves heat radiation efficiency totally. It is easily suggested that base plate 2a should be thickened simply in order to improve a thermal diffusion effect of the heat conducting unit in FIG. 14A. However, the unit needs to be rather thick, thereby increasing the weight of the heat sink.
When a cooling fan is disposed on a heat sink as shown in FIG. 16A, sufficient space is required over the cooling fan. However, as electronic apparatuses have been recently downsized, additional structure 19 is often disposed over the cooling fan. Sufficient upper clearance (d) over the fan cannot always be secured. FIG. 16B is a graph showing a relation between heat radiation performance and the clearance over the fan. The vertical axis of this graph represents a ratio of heat radiation performance W/W max (normalized heat radiation performance), and the horizontal axis represents a ratio d/d max (normalized upper clearance) of the clearance over the fan, where W is heat radiation performance corresponding to the clearance (d) over the cooling fan, and W max is a maximum heat radiation performance obtained when heat radiation performance W becomes constant in relation to a gradual increase of clearance (d) over the fan from zero. A clearance obtained at this time is d max. The graph shows that the heat radiation performance declines as the clearance over the cooling fan decreases.
A small and light heat sink has high radiation performance for radiating heat generated from a heating element, even for a downsized electronic apparatus. A small cooling apparatus employs the heat sink and has high cooling performance. A method of manufacturing an inexpensive heat sink having high performance at a high productivity is further provided.
The heat sink for radiating the heat generated from the heating element includes a heat conducting plate having a heat receiving surface facing the heating element, and plural fins disposed on the upper surface, which is opposite to the heat receiving surface, of a heat conducting plate in nonparallel relation with the heat receiving surface. The heat conducting plate has a thickness that increases from a first end of the heat receiving surface toward a second end opposite to the first end in vertical cross section (i.e. cross section perpendicular to the heat receiving surface).
The cooling apparatus includes the heat sink and a cooling device mounted to the heat sink.
In the method of manufacturing the heat sink, the heat conducting plate and first slits, which define vertical fins therebetween (i.e. fins that are perpendicular to the direction from the first end to the second end of the heat receiving surface) are simultaneously formed.